Cylindrical shaped snorkel interface on evaluation probe

Abstract

A snorkel and pad for use with a formation testing tool is formed with a cylindrical geometry at the interface where the snorkel and pad contacts the inner surface of a borehole. The cylindrical geometry reduces or eliminates gaps that a flat interface surface would leave between the snorkel and the inner surface of the borehole, reducing the possibility that a surrounding pad could extrude through the gap. The snorkel is prevented from rotating during operation, ensuring the correct orientation of the cylindrical geometry interface surface relative to the inner surface of the borehole. The snorkel may be used as part of a formation testing system.

What is claimed is: 
     
       1. A method, comprising:
 reducing an extrusion gap between a borehole interface surface of a first snorkel of a formation testing tool and a surface of a borehole, comprising:
 forming a cylindrical geometry at a borehole interface of the first snorkel; 
 extending the first snorkel through an opening in a protective pad disposed about the first snorkel, 
 
 wherein the cylindrical geometry is operationally axially aligned parallel to a longitudinal axis of the borehole. 
 
     
     
       2. The method of  claim 1 ,
 wherein the cylindrical geometry has a radius determined by a radius of the borehole. 
 
     
     
       3. The method of  claim 1 , further comprising:
 replacing the first snorkel with a second snorkel having a cylindrical geometry with a different cylindrical radius. 
 
     
     
       4. The method of  claim 1 ,
 wherein the pad has a cylindrical geometry having a radius determined by a radius of the borehole. 
 
     
     
       5. The method of  claim 4 , wherein the act of forming a cylindrical geometry at a borehole interface of the first snorkel further comprises:
 disposing a support element with the pad, the support element having a cylindrical geometry oriented parallel to the longitudinal axis of the borehole. 
 
     
     
       6. The method of  claim 1 , further comprising:
 preventing rotation of the first snorkel relative to the borehole. 
 
     
     
       7. The method of  claim 6 , wherein the act of preventing rotation of the first snorkel relative to the borehole comprises:
 keying a body of the first snorkel; 
 inserting the first snorkel into a piston cylinder; and 
 preventing rotation of the body of the first snorkel relative to the piston cylinder with an anti-rotation pin. 
 
     
     
       8. The method of  claim 6 , wherein the act of preventing rotation of the first snorkel relative to the borehole comprises:
 forming a body of the first snorkel with a non-circular cross-section. 
 
     
     
       9. A snorkel for use in a formation testing tool, comprising:
 a tubular body, configured for extension from and retraction into a piston cylinder of the formation testing tool, wherein the tubular body when extended from the piston cylinder, extends through an opening in a pad; and 
 a borehole interface, formed at a radially outward and of the tubular body, having a cylindrical geometry, 
 wherein the cylindrical geometry of the borehole interface is operationally axially aligned parallel to a longitudinal axis of the borehole. 
 
     
     
       10. The snorkel of  claim 9 , wherein the tubular body is substantially circular in cross-section. 
     
     
       11. The snorkel of  claim 9 , wherein the tubular body is keyed to prevent rotation of the tubular body relative to the piston cylinder. 
     
     
       12. The snorkel of  claim 11 , further comprising:
 an anti-rotation pin, disposed with the tubular body and the piston cylinder, wherein the anti-rotation pin prevents rotation of the tubular body relative to the piston cylinder. 
 
     
     
       13. A system for testing an earth formation surrounding a borehole, comprising:
 a formation testing tool, comprising:
 a plurality of sections, at least one of which comprises:
 a piston cylinder; and 
 a first snorkel configured for extension from and retraction into the piston cylinder, comprising:
 a tubular body, configured for extension from and retraction into the piston cylinder; 
 a pad, disposed about the tubular body, wherein the tubular body extends through an opening in the pad when extended from the piston cylinder; and 
 a borehole interface, formed at a radially outward end of the tubular body, having a cylindrical geometry, 
 wherein the cylindrical geometry of the borehole interface is operationally axially aligned parallel to a longitudinal axis of the borehole; 
 
 
 
 a conveyance apparatus; and 
 a connecting structure operationally connecting the formation testing tool to the conveyance apparatus to convey the formation testing tool in the borehole. 
 
     
     
       14. The system of  claim 13 , wherein a radius of the cylindrical geometry is configured to correspond to a radius of the borehole. 
     
     
       15. The system of  claim 13 , wherein the first snorkel is replaceable with a second snorkel wherein the borehole interface of the second snorkel has a cylindrical geometry with a different cylindrical radius than the cylindrical radius of the cylindrical geometry of the borehole interface of the first snorkel. 
     
     
       16. The system of  claim 13 , wherein the tubular body is substantially circular in cross-section. 
     
     
       17. The system of  claim 13 , wherein the tubular body is keyed to prevent rotation of the tubular body relative to the piston cylinder. 
     
     
       18. The system of  claim 17 , wherein the first snorkel further comprises an anti-rotation pin, disposed with the tubular body and the piston cylinder, wherein the anti-rotation pin prevents rotation of the tubular body relative to the piston cylinder. 
     
     
       19. A formation testing tool, comprising:
 a plurality of sections, at least one of which comprises:
 a pad, comprising:
 an elastomeric element, configured for sealing with a surface of the borehole; and 
 
 a piston cylinder; and 
 a first snorkel configured for extension from and retraction into the piston cylinder, the pad disposed about the first snorkel, the first snorkel comprising:
 a tubular body, configured for extension from and retraction into the piston cylinder, wherein the tubular body when extended from the piston cylinder, extends through an opening in the pad; and 
 a borehole interface, formed at a radially outward end of the tubular body, having a cylindrical geometry, 
 wherein the cylindrical geometry of the borehole interface is operationally axially aligned parallel to a longitudinal axis of the borehole. 
 
 
 
     
     
       20. The formation testing tool of  claim 19 , wherein the first snorkel further comprises an anti-rotation pin, disposed with the tubular body and the piston cylinder, wherein the anti-rotation pin prevents rotation of the tubular body relative to the piston cylinder. 
     
     
       21. The formation testing tool of  claim 19 , wherein the first snorkel is replaceable with a second snorkel wherein the borehole interface of the second snorkel has a cylindrical geometry with a different cylindrical radius than the cylindrical radius of the cylindrical geometry of the borehole interface of the first snorkel. 
     
     
       22. The formation testing tool of  claim 19 , further comprising:
 a support element, disposed between the elastomeric element and the first snorkel, having a cylindrical geometry that is operationally axially aligned parallel to a longitudinal axis of the borehole.